This invention relates to disc drives, and particularly to techniques for active damping of two-stage actuator systems in disc drives.
The actuator system of disc drives includes a rigid extended actuator arm that supports a flexible suspension at the distal end of the arm, with the suspension supporting an aerodynamic slider arranged to xe2x80x9cflyxe2x80x9d over an associated storage disc surface. The slider includes a transducing head arranged to read data from and write data to concentric tracks on the disc. A voice coil motor operates the actuator arm to rotate about an actuator arm axis outside the periphery of the disc to thereby move the slider and head to selected radial positions adjacent data tracks on the disc.
As the track density within disc drives increases, the radial distance between track centers on the discs decreases. As a result, it has been increasingly difficult for traditional voice coil motors to accurately operate the actuator arm to position the head over the center of a selected track. For this reason, microactuators have been employed in the arm, suspension or slider, to fine position the head. The voice coil motor is employed to coarsely position the transducing head in relation to the track, and track following and fine positioning is accomplished using the microactuator. Examples of microactuators in the arm, suspension and slider can be found in U.S. Pat. No. 5,898,541 granted Apr. 27, 1999 to Zine-Eddine Boutaghou and Lowell J. Berg, U.S. Pat. No. 6,052,251 granted Apr. 18, 2000 to Khosrow Mahajerani, Joseph M. Sanpietro, Anoush M. Fard, Jeffrey G. Barina, Muhammad A. Hawwa, LeRoy A. Volz, Tien Q. Le and Daniel R. Vigil, and U.S. Pat. No. 6,069,771 granted May 30, 2000 to Zine-Eddine Boutaghou and Joseph C. Liu, all assigned to the same assignee as the present invention. Disc drive actuator systems using both voice coil motors and microactuators are known as dual-stage or two-stage actuator systems.
Track seeking with a two-stage actuator system is described in U.S. Pat. No. 5,978,752 granted Nov. 2, 1999 to John C. Morris and assigned to the same assignee as the present invention. Track seeking with a two-stage actuator system is performed by operating the voice coil motor move the actuator system in accordance with a seek profile selected by the disc controller. The seek profile defines the velocity and position of the actuator arm as it moves the head from the start track to the destination track. The controller derives an actuator signal based on the selected seek profile to operate the voice coil motor. The voice coil motor moves the actuator arm to coarsely position the head relative to the destination track. The controller then operates the microactuator to fine position the head and to perform track following functions.
Structural resonance within the disc drive, and particularly within the actuator system during a seek, adversely affects the seek operation, causing the actual seek position and velocity profile to be different from that selected by the controller. Consequently, it is common to monitor the track position and profile compensate the actuator signal to actively damp the resonance of the actuator system and achieve a smooth seek profile. However, the compensation to the actuator signal, and the seek itself, introduces delay to the seek operation. Moreover, aggressive seek profiles cause oscillation during settling. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
The present invention is directed to an actuator control system for a two-stage actuator system of a disc drive. The actuator system has a first, or primary, stage actuator consisting of a voice coil motor that positions the head supported by the actuator system relative to a disc. The actuator system includes a microactuator that alters the actuator system without operation of the voice coil motor, such as by moving the slider relative to the suspension, by moving the suspension relative to the actuator arm, or by distorting the actuator arm. The actuator control system includes a control loop that is responsive to seek commands to provide an actuator signal that operates the voice coil motor, thereby moving the head relative to the disc. Means is responsive to the position signals to operate the microactuator to damp resonance modes of the actuator system. In preferred embodiments, the control loop further includes a summing device responsive to position signals from the head to modify the actuator signal.
The actuator system includes an actuator arm arranged to rotate about an actuator axis, and a suspension coupled to an end of the actuator arm, a slider coupled to the suspension supporting a head adjacent a disc. The voice coil motor is coupled to the actuator arm and is operable to rotate the actuator arm about the actuator axis to thereby adjust a position of the head relative to the disc. The microactuator is supported on at least one of the actuator arm, suspension and slider, and is operable to adjust the position of the head relative to the disc without operation of the voice coil motor. The actuator control system includes a controller responsive to the seek commands for providing an actuator signal to operate the voice coil motor to move the head relative to the disc. An active damping circuit is coupled to the head to operate the microactuator to damp resonance modes of the actuator system.
In one form of the invention, a process is provided to actively dampen a two-stage actuator system of a disc drive during a seek operation. An actuator signal, based on a seek command, is applied to the voice coil motor to move the head supported by the actuator system. The microactuator on the actuator system is operated based on position signals from the head during the seek operation to damp resonance modes of the actuator system.
Other features and benefits that characterize the present invention will be apparent upon reading the following detailed description and review of the associated drawings.